1. Field of the Invention
The present invention relates generally to the delivery of communication services to subscribers via a communication network and, more particularly, to the transmission of signals within a hybrid fiber coax transmission system.
2. Discussion of the Background Art
Conventional cable television (CATV) systems utilizing a hybrid fiber coaxial (HFC) architecture typically provide downstream broadcast information from a headend or primary hub to optical access nodes for multiple CATV channels using analog (AM-VSB) broadcast signals from about 50 MHz to 350 MHz, 550 MHz, or even 750 MHz. While upgrading from 550 or 750 MHz has allowed system owners to increase revenue by boosting the channel capacity of the coaxial cable portion of their systems and to thereby provide additional services such as premium and pay-per-view channels, each such upgrade requires re-engineering the entire cable plant including at least amplifier replacement and associated amplifier spacing. Further, many conventional system operators also want to provide broadcast digital signals, as well as broadcast analog signals over a single transmission line. However, this is difficult, as impulse noise caused by the analog signals can cause errors in the digital signals. See for example, S. Ovadia and Chinlon Lin (invited paper), xe2x80x9cPerformed Characteristics and Applications of Hybrid Multichannel AM-VSB/M-QAM Video Lightwave Transmission Systemsxe2x80x9d, IEEE J. Lightwave Tech., 16, 1171 (July, 1998).
As a further means of increasing revenue, and as part of an overall strategy of competing in a field where an operator""s continued viability may well depend on an ability to deliver a wide range of services to as many market segments as possible, a few CATV systems owners have sought to expand their subscriber base beyond the traditional residential consumer of broadcast video services. As part of this strategy, CATV system owners have sought to attract and retain small-, medium-, and even large-sized business customers. Such expansion depends, in large part, on an ability to deliver reliable, bi-directional transport of digital signalsxe2x80x94at substantially higher data rates than are presently offered to or demanded by typical residential subscribers. Heretofore, such system owners have sought to address this market segment by creating separate operating subsidiaries and deploying new infrastructure similar to those used by traditional local exchange carriers. It should be readily apparent that such a strategy, in which the cable company invests the same resources as any other market entrant (i.e., an independent local exchange carrier), yields no intrinsic competitive advantage to the HFC network owner/operator.
A trend which presents a significant opportunity to the hybrid fiber coax system operator is the proliferation of home based businesses and telecommuters with an increasing appetite for high capacity, bidirectional bandwidth. Unfortunately such needs are not adequately addressed by the so-called cable modem subscription service presently offered, due to its limited bandwidthxe2x80x94which actually decreases as new subscribers are addedxe2x80x94and it is expected that the growth in demand for capacity by such xe2x80x9chome officexe2x80x9d users will only accelerate over time.
There do now exist HFC systems that provide two-way transmission of information, e.g., video, audio, multimedia, and/or data, between a headend and a plurality of subscribers. Typically, the headend transmits the information destined for individual subscribers (xe2x80x9cdownstream informationxe2x80x9d) in a wavelength division multiplexed optical format, via one or more optical links, to one or more optical access nodes. Each fiber node converts the optically formatted downstream information into electrical signals for distribution, via a coaxial cable plant having a tree and branch architecture to individual subscribers. In addition to receiving the downstream information, each individual subscriber may generate information, in the form of voice, video, data, or any combination thereof, destined for the headend. The subscriber generated information (xe2x80x9cupstream informationxe2x80x9d) is aggregated by the coaxial cable plant and passes to the optical access node for conversion into an optical format for transmission to the headend. The bandwidth (e.g., 5-40 MHz) associated with the upstream information is shared by all subscribers served by the same optical access node. As such, while this arrangement may be well suited to the delivery of bidirectional communication services to residential subscribers, it does not address the high bandwidth needs of the typical home-business customer.
More advanced systems being deployed or contemplated by traditional telephone carriers include the so-called Fiber-To-The-Home (FTTH) architecture, in which optical signals are exchanged between a central office and the homes of residential telephone service subscribers via a network of optical fiber links. Although such systems are quite attractive in terms of their ability to deliver a wide array of individually customized telecommunications services, the associated capital cost remains the most significant disincentive for their widespread deployment by local cable providers. While some subscribers would undoubtedly be willing to pay a higher price for access to a more sophisticated telecommunications network, at present such interest has not been deemed sufficiently high by cable system operators to warrant a total replacement of their existing infrastructure.
Accordingly, there exists a need for a hybrid fiber coax (HFC) network architecture, and method of upgrading and operating the same, which allows the owner or operator of a hybrid fiber coax network to gradually and strategically extend the benefits of a FTTH network as it attracts the subscribers willing to pay for them, while still deriving the maximum benefit of its existing infrastructure. Such an architecture, initially comprising what might be better termed a Fiber To The Home Office (FTTHO) network architecture, would advantageously provide a graceful upgrade path which, ultimately, would culminate in a state-of-the-art FTTH network.
The aforementioned needs are addressed, and an advance is made in the art, by a hybrid fiber coaxial cable (HFC) network incorporating a multiple wavelength overlay to deliver Fiber to the Home Office (FTTHO) services alongside traditional residential subscription services over coaxial cable. First wavelength division multiplexed (WDM) optical signals corresponding to a first category of subscriber service are directed, via a fiber portion of the transmission system, from a headend to a plurality of fiber nodes for conversion to respective electrical signals. The converted electrical signals are transmitted via a coaxial cable portion of the transmission system to individual subscribers. Second WDM optical signals corresponding to a second category of subscriber service are exchanged, via a fiber portion of the transmission system, between a headend and at least one of the individual subscribers, by demultiplexing them and transmitting them to such individual subscribers over optical fibers (i.e., without first converting them to electrical signals and without using the existing coaxial cable plant). As more subscribers opt for the enhanced, FTTH service accommodated by the dual attachment of coaxial cable and optical fiber to the nearest network node, a suitable multiplexing technique such, for example as time division multiplexing (TDM), may be employed to allow many homes to be served by each demultiplexed wavelength. For newer construction, the need to further extend the coaxial plant may be obviated, with the new homeowners receiving fiber to the home service when they move in. In this way, the benefits of a FTTH system may be extended in a strategic manner only where it is economically feasible to do so, starting with those residential and/or home-based business subscribers having a present need and/or desire for them.
In accordance with an especially preferred embodiment of the present invention, the first WDM optical signals are within a first wavelength band and the second WDM optical signals are within a second wavelength band different from the first wavelength band. By way of illustrative example, the first wavelength band may be between from about 1530 nm to about 1560 nm, and the second wavelength band may be between from about 1570 nm to about 1610 nm.
Other objects, advantages, and features of the invention will become apparent from the detailed description taken in conjunction with the annexed drawings, which depict illustrative embodiments of the invention.